We have two independent checks for "is this attribute unsafe"

[RalfJung]

Turns out #123757 was implemented by duplicating existing information previously added for #82499:

• Attributes are marked as unsafe here:

rust/compiler/rustc_feature/src/builtin_attrs.rs

Lines 431 to 433 in 624c071

	ungated!(unsafe export_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding, EncodeCrossCrate::No),
	ungated!(unsafe link_section, Normal, template!(NameValueStr: "name"), FutureWarnPreceding, EncodeCrossCrate::No),
	ungated!(unsafe no_mangle, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),

• But separately, the unsafety checker has a list of unsafe attributes here:

rust/compiler/rustc_lint/src/builtin.rs

Lines 293 to 303 in c682aa1

	if let Some(attr) = attr::find_by_name(&it.attrs, sym::no_mangle) {
	self.report_unsafe(cx, attr.span, BuiltinUnsafe::NoMangleFn);
	}
	if let Some(attr) = attr::find_by_name(&it.attrs, sym::export_name) {
	self.report_unsafe(cx, attr.span, BuiltinUnsafe::ExportNameFn);
	}
	if let Some(attr) = attr::find_by_name(&it.attrs, sym::link_section) {
	self.report_unsafe(cx, attr.span, BuiltinUnsafe::LinkSectionFn);
	}

and here:

rust/compiler/rustc_lint/src/builtin.rs

Lines 307 to 317 in c682aa1

	if let Some(attr) = attr::find_by_name(&it.attrs, sym::no_mangle) {
	self.report_unsafe(cx, attr.span, BuiltinUnsafe::NoMangleStatic);
	}
	if let Some(attr) = attr::find_by_name(&it.attrs, sym::export_name) {
	self.report_unsafe(cx, attr.span, BuiltinUnsafe::ExportNameStatic);
	}
	if let Some(attr) = attr::find_by_name(&it.attrs, sym::link_section) {
	self.report_unsafe(cx, attr.span, BuiltinUnsafe::LinkSectionStatic);
	}

and here:

rust/compiler/rustc_lint/src/builtin.rs

Lines 336 to 341 in c682aa1

	if let Some(attr) = attr::find_by_name(&it.attrs, sym::no_mangle) {
	self.report_unsafe(cx, attr.span, BuiltinUnsafe::NoMangleMethod);
	}
	if let Some(attr) = attr::find_by_name(&it.attrs, sym::export_name) {
	self.report_unsafe(cx, attr.span, BuiltinUnsafe::ExportNameMethod);
	}

This should be cleaned up into a single source of truth for which attributes are unsafe.